Radio communications systems are known in which radio stations (commonly using transceivers) communicate with each other via a repeater which establishes a communication channel between the radio stations. The radio stations of the system are divided into a plurality of groups. Radio stations belonging to any one group may communicate freely with other radio stations in the group. In addition, if the repeater is equipped with a telephone interconnect network, the radio stations of a group may communicate with telephones outside of the group. Each radio station has an identification tone signal. The identification tone signal may be a group of sequential tones which simultaneously identifies all radio stations belonging to a single group. Alternatively, the identification tone signal may be a sub-group signal or an individual identification signal identifying subsets of the group or individual radio stations within the group.
A radio station may establish communications with one or more other radio stations by transmitting the identification tone signals of such other radio stations. Radio stations not actively engaged in communications may monitor one or more communications channels, awaiting the identification tone signals assigned to them. When a radio station receives an identification tone signal assigned to it, it may participate in communications on the channel.
Each radio station may "possess" one or more identification tone sequences (the identification tones assigned to each radio station determining which stations may be contacted by that radio station). Thus, a radio station possessing identification tones for a first and second group of radio stations may contact any radio station(s) within the first or second group, but may not contact radio stations in other groups. Each radio station may also possess sub-group and/or individual identification tones. Thus, a radio station may contact all members of another group if it possesses the identification tones for that group. The radio station may contact an individual member of a group if it possesses the individual identification tone of that member. A radio station is restricted to contacting only those stations for which it "possesses" (is programmed with) the identification tones (group tones, sub-group tones, and individual identification tones).
However, if the repeater is equipped with a telephone interconnect network, any radio station may freely communicate with any telephone outside of the group. Thus, asymmetry exists between the ability of a radio station to contact telephones outside of his group and to contact mobile radio stations outside of his group.
Such radio communications systems are disclosed in the following patents which are specifically incorporated herein by reference; U.S. Pat. No. 4,360,927 to Bowen et al issued on Nov. 23, 1982 entitled a "Repeater Trunking System"; U.S. Pat. No. 4,347,625 to Williams issued on Aug. 31, 1982 entitled "Arrangement for Cellular Operation of a Repeater Trunking System"; and U.S. Pat. No. 4,409,687 to Berti et al issued on Oct. 11, 1983 entitled "Arrangement and Method for Establishing Radio Communications in a System".
FIG. 1 is a pictorial diagram indicating the various modes of operation of a mobile radio station, as described in the above referenced patents. The operation of the mobile transceiver may be broken down into the functional modes (states) of "idle", "wait", and "ready". When power is initially applied to a mobile station, the radio station is placed in the idle mode. In the idle mode, a radio station continuously scans the communication channels for a call identifying the particular group with which it is associated. Thus, the radio station looks for identification tone sequence signals with which that radio station is associated. All audio circuits of the mobile station are inhibited in this mode so that the user is undisturbed. If a call is decoded indicating that a particular mobile station is within a group being called, that radio station is placed in a ready mode. In the ready mode, the radio station is locked onto a channel and ready to communicate. The audio circuits are enabled and an indicator lamp (not shown) is illuminated. An audible alarm (such as four alert beeps) is sounded by the radio station upon entry of the radio station into the ready mode in order to alert an operator that a call has come in.
If the repeater which has caused the mobile station to lock onto the channel goes off the air, or communication is otherwise interrupted, the radio station returns to the idle mode from the ready mode and resumes searching for calls identifying a particular group with which it is associated.
From the idle mode, if a user desires to originate a call (such as by depressing a push-to-talk (PTT) button located on, for instance, a hand-held microphone), the radio station operates in the wait mode. In the wait mode, the station stops scanning on the first idle one of the communication channels and attempts to acquire the corresponding repeater. Channel acquisition signalling protocol may be that described in commonly-assigned application Ser. No. 721,815 filed Apr. 10, 1985, or that described in U.S. Pat. No. 4,360,927 to Bowen et al. For instance, the station may send a busy signal to the repeater and wait to hear an acquisition signal. During this procedure, an indicating lamp is illuminated and the audio circuits of the mobile station are disabled. After all channels have been tried without acquiring a repeater, the radio station may inform the user that no idle communication channels are available (for instance, by sounding an audible beep).
If all channels are busy or if the mobile station has failed to establish communication with a repeater, the radio station returns to the idle mode. However, if a repeater is acquired, the radio station proceeds to transmit the desired identification signals.
FIG. 2 depicts a prior art system in which repeater network 11 establishes communications between the various stations of Groups 1, 2 and 3. Group 1, may, for example, be a fleet of oil delivery trucks, each truck containing a mobile radio. Likewise, Group 2 may be a fleet of gasoline delivery trucks and Group 3 may be a telephone answering service for Groups 1 and 2.
As depicted in FIG. 2, vehicle 1A can establish communications with vehicle 1B and/or 1C via repeater R-1 over a communications channel. Vehicle 1A uses the Group 1 tones and/or individual identification tones for contacting vehicles 1B and/or 1C. At the same time, vehicle 2A may communicate with telephone 3A via repeater R-4 and telephone interconnect network 13. However, vehicles from Group 1 are prohibited from communicating directly with vehicles from Group 2 because the Group 1 vehicles are not programmed to transmit identification tone signals of Group 2 and therefore cannot establish communications with them.
FIG. 3 depicts one method by which vehicles from Group 1 may establish radio contact with vehicles from Group 2 without transmitting the Group 2 tones. Such a method begins with vehicle 1A establishing communications with the repeater network 11 through repeater R-1. Vehicle 1A then requests a telephone line through the telephone interconnect network 13. Once the telephone line is granted, vehicle 1A requests to be connected to another telephone line within the same telephone interconnect network 13. Once this connection is made, vehicle 1A requests that communication be established with vehicle 2A through repeater R-4. Such a method, while workable, is expensive since it requires the use of two repeaters and two telephone lines to establish inter-group communications. In addition, once communication is established between vehicle 1A and vehicle 2A, no additional radio stations may be brought into this communication channel unless they belong to Groups 1 or 2.
U.S. Pat. No. 4,347,625 (referred to above) describes a system in which mobile radio stations of Group 1 can establish contact with mobile radio stations of Group 2. In such a system, vehicle 1A is programmed to selectively transmit the identification tones of vehicle 2A and/or Group 2. Thus, in such a system radio communications may be established between vehicles 1A and 2A by using a single repeater and a single communications channel. However, a limitation of such a system is that once communication is established between vehicles 1A and 2A, no additional radio stations, outside of Group 2, may be called onto the communication channel.
Thus, in the prior art, no method or apparatus exists which permits a plurality of radio stations from a plurality of groups to be brought onto a single communication channel after communication has been established between two or more stations.
Therefore, an object of the present invention is to provide method and apparatus by which a radio station which has an established communication channel (i.e., is communicating over a communications channel) with another station may dispatch overdial additional stations belonging to other groups so that a plurality of radio stations belonging to a plurality of groups may all communicate on the same communication channel.
Another object of the present invention is to provide a control method and apparatus by which such dispatch overdialing may be restricted to those members of the group which first established the communication channel. This feature prevents vehicles which have been dispatch overdialed onto the communication channel from themselves dispatch overdialing radio stations in other groups and having the communications thus established billed to the group which originally established the communication channel.
Another object of the present invention is to provide a control method and apparatus by which a vehicle which has been dispatch overdialed onto the communication channel is allowed to dispatch overdial radio stations in other groups. However, such dispatch overdial calls can be billed to the dispatch overdialing radio station instead of the group which originally established the communication channel.
Another object of the present invention is to provide method and apparatus in which a radio station from a given group may dispatch overdial a plurality of mobile radio stations and a plurality of telephones so that all mobile radio stations and all telephones can communicate on the same channel.